Simplify ttHitAverage away

Simplify ttHitAverage away

Simplify ttHitAverage away, which was introduced in the following commit:
[here](https://github.com/BM123499/Stockfish/commit/fe124896b241b4791454fd151da10101ad48f6d7)

A few tweaks with Elo gaining bounds have been tried to keep the code,
but they all failed:
https://tests.stockfishchess.org/tests/view/61656f7683dd501a05b0b292
https://tests.stockfishchess.org/tests/view/6165c0ca83dd501a05b0b2ca
https://tests.stockfishchess.org/tests/view/6165bf9683dd501a05b0b2c8
https://tests.stockfishchess.org/tests/view/6165719483dd501a05b0b29b
https://tests.stockfishchess.org/tests/view/6166c7fd83dd501a05b0b353
https://tests.stockfishchess.org/tests/view/6166c63b83dd501a05b0b350

STC:
LLR: 2.94 (-2.94,2.94) <-2.50,0.50>
Total: 58504 W: 14781 L: 14694 D: 29029
Ptnml(0-2): 175, 6718, 15426, 6711, 222
https://tests.stockfishchess.org/tests/view/6165112c83dd501a05b0b257

LTC:
LLR: 2.96 (-2.94,2.94) <-2.50,0.50>
Total: 33480 W: 8448 L: 8332 D: 16700
Ptnml(0-2): 21, 3569, 9447, 3679, 24
https://tests.stockfishchess.org/tests/view/61656fcf83dd501a05b0b294

change https://github.com/official-stockfish/Stockfish/pull/3739

bench: 4540339